The Ospreys moved back to the top of the Magners League with an emphatic victory over their close rivals and served notice to Clermont Auvergne and Leicester that they will be the team to beat when the Heineken Cup resumes this month. There is a growing authority about a side that has too often melted under pressure in the past. They were mentally and physically stronger than the subdued Blues.

Dan Biggar will be the beneficiary if the Wales fly-half Stephen Jones's shoulder injury proves more serious than his region, the Scarlets, believe, after the 32-year old left the field early against Newport Gwent Dragons this week. Here, Biggar gave the Ospreys the lead with a snap drop goal and controlled the game with a growing imperiousness. The Ospreys prefer Biggar to James Hook at No10 because he takes fewer risks and is more voluble, traits the Wales coaches admire above art and craft. Hook was absent here with a shoulder injury that is expected to keep him out for another week and a typically full-blooded derby missed his subtle touches.

The Blues, yet to win away in the league this season, started brightly with Casey Laulala and Sam Norton-Knight showing neat touches, but with most scrums ending in free-kicks or penalties the game stagnated. Handling was not helped when it started snowing heavily. The Ospreys exploited their forward power and their Scotland wing, Nikki Walker, scored the first try on 20 minutes after Andrew Bishop had forced a turnover from Ben Blair in the Blues' 22. Walker was soon diving over in the same spot after Biggar broke from a scrum and released his outside backs with a reverse left-handed pass.

The Blues were fortunate to only trail 13-0 at the break. They threatened the Ospreys' line once, when Richard Mustoe was tackled into touch two yards out, and their midfield was defensively suspect before Tom Shanklin limped off after 33 minutes.

Biggar kicked two penalties in the opening minutes of the second half and Blair hit the post with a 40-yard attempt, before the Blues prop Gary Powell was shown a yellow card for collapsing, the 15th scrum infringement of the game. After yet another scrum penalty, Ryan Jones scored in the left-hand corner to put his side out of sight.